I've heard this multiple times, yet I get the opposite picture at any supermarket. Buying about 14k calories of well-balanced food (oats, bread, high-protein cheeses, some meat, some veggies, fruit, nuts, noodles, yoghurt, milk, whatever) costs me around 30 Euro. Suppose I could've bought nothing but 5kg of the cheapest wiener sausages to get that same number of calories, but even they are 6 Euro/kg, so exactly the same price.
Getting 14k calories buying BigMacs at McDonald's would've cost me 150 Euro (6 Euro / 500kcal).
What the fuck are people buying to live unhealthily for less? Raw sugar? Since you also mentioned "most addictive", I now picture that people have diets consisting mostly of candy. Cheap candy.
The fact remains that a healthy diet is perfectly affordable - I can cover the basics for less than 150 Euro / month, and I'm not price conscious, even opting for the expensive options in the fruit/vegetable department. That amount of money is nothing in a country where the minimum wage is 1600 Euro / month (4k/mo average).
So yes, I'd tentatively agree on "addictive", but not so much on "expensive". At the end of the day humans are supposed to be 'addicted' to food - it's called hunger. Eating oats will get rid of that craving just like eating gummy bears will, but the gummy bears are just bad decision-making. You had to physically go out of your way to buy those over something else, just so you had them on you the next time you are hungry.